The present invention relates to a dual band electronic scanning antenna with an active microwave reflector. It is applicable especially to microwave applications requiring two transmission bands moreover subject to very low-cost production conditions. It may for example be applicable to individual stations for communicating with non-synchronous satellites, and more generally, for numerous types of multimedia applications.
It is known to produce antennas comprising an active microwave reflector. The latter, also known as a xe2x80x9creflect arrayxe2x80x9d, is an array with electronically controllable phase shifters. This array lies in a plane and comprises an array of phase-control elements, or phased array, placed in front of the reflecting means, constituted, for example, by a metal plane forming an earth plane. The reflecting array especially comprises elementary cells, each one producing the reflection and phase shifting, which can be varied by electronic control, of the microwave that it receives. Such an antenna provides considerable beam agility. A primary source, for example a horn placed in front of the reflecting array, transmits the microwaves toward the latter.
Mass applications can be envisioned for such antennas, in particular with the advent of interactive multimedia activities via satellite communications networks. In order to provide continuity of a communications network, non-synchronous satellites are placed around the earth. The ground antennas must track the satellites. In order to switch from one satellite to another without phase jumps, the antennas transmit and receive over two frequency bands, with different phase shifts between these two bands.
One aim of the invention is the production of a dual-band electronic scanning antenna with a reflecting array intended in particular for mass applications, and therefore with a low production cost.
To this end, the subject of the invention is an electronic scanning antenna, characterized in that it comprises at least two microwave sources transmitting in different frequency bands and having opposite circular polarizations, an active reflecting array comprising elementary cells illuminated by the sources and a polarization rotator, inserted between the reflecting array and the sources, changing the circular polarizations into two crossed linear polarizations, an elementary cell comprising two transverse phase shifters, the first phase shifter acting on the waves of one linear polarization and the second phase shifter acting on the waves of the other linear polarization.